-irreversible ACHe inhibitor
-rapidly metabolized by birds and mammals to non-toxic metabolites but not by insects or fish
-parathion is not detoxified in vertebrates, more dangerous

nerve agents

sarin, soman, tabun and vx
-chemical warfare
-flaccid paralysis, respiratory failure
-pyridostigmine given prophylactically to block binding of irreversible agents so more time for tx with atropine or 2-PAM